Wire feeding systems are commonly used for feeding welding wires from a supply source, for example a container in which a significant amount (up to several hundred kilograms) of welding wire is being stored, to a point called welding arc where the welding wire is being deposited through a welding torch, with the purpose of joining metal parts. Since the welding torch is usually connected to a welding robot and continuously moving, the welding wire has to be fed through a wire guiding liner conduit from the container to the welding torch. The passing of the welding wire through the inevitable bends and curvatures on the wire guiding liner conduit necessarily creates a certain amount of friction and drag. More curves along the wire guiding liner conduit can worsen the problem to the point that it becomes very difficult for the wire feeding system to function properly and to guarantee the necessary smooth feeding.
In conventional welding applications, a single feeding device pulls the wire from the container and feeds it to the welding torch and it is placed between the wire storage or source (the container) and the welding torch (the consumer). In some other welding applications the feeding device itself contains the wire source in the form of a small spool and feeds the wire to the welding torch.
In robotic and automated applications, which are designed to maximize the productivity, the trend goes towards using large bulk packs containing from few hundred kilograms to more than one ton of welding wire. These bulk containers have to be positioned in a safe area at a significant distance from the device feeding the welding wire to the welding torch and preferably on the floor in a location that can be easily accessed by a forklift. In order to comply with increasingly stricter safety regulations and standards, it is strongly advisable to refrain from placing containers with welding wire high on top of traveling robots, where the maneuver of replacing a used pack with a new one can represent a serious hazard for the robot operators and weight tolerances would only permit the use of containers carrying a limited quantity of welding wire. Placing the packs at the floor undoubtedly offers the significant advantages of making it possible to use heavier containers with more product, for a maximized downtime saving, and of working in a safer environment but it can result in the welding wire having to be pulled over significant distances by the front feeder device from bulk containers towards the welding torch.
Transporting and feeding welding wire over long distances, preferably through guiding liner conduits placed for convenience inside the cable drag chains is not an easy task and often the main pulling wire feeder close to the welding torch is not capable of reliably advancing the welding wire. To assist the front pulling feeder, systems are known which use the combined action of a so-called master feeder (the wire feeding device close to the welding torch) and a so-called slave wire feeder (a second wire feeder installed remotely from the welding torch, close to the wire supply bulk container). Both wire feeders are controlled by a common unit or are controlled by using the same data source. E.g. both wire feeders are equipped inside with the software and hardware necessary to synchronize their movements so that the welding wire is being fed to the welding torch by the combined pulling effect of the master feeder and the pushing assistance of the rear slave feeder. This interaction between the two units is possible because both are normally supplied by the same manufacturer and communicate using the same protocols but this represents, for the market, a limitation of competitiveness and an increase of costs for the end users. For example, the control data which are used to control the front pulling feeder are also sent to the slave wire feeder so that both feeders are synchronized by using the same data source.
In the attempt to reduce the dependence from the master and slave feeder manufacturers, less advanced systems are known which employ a so-called feed assisting booster that operates independently from the main wire feeder close to the welding torch. The assisting booster is not coupled with the front pulling feeder or the torch, i.e. signals for controlling the front pulling feeder or the torch are not used for controlling the rear feed assisting booster, which instead detects when the wire feeder is pulling welding wire, and then automatically engages through a mechanically controlled clutch or a similar mechanical device. However, the action of the wire feeder close to the welding torch assisted by the independent feeding booster is not as reliable and efficient as the combined synchronized cooperation of master and slave feeding systems. This is due to the fact that the booster feeder always reacts with a certain delay, which increases proportionally with the length of the wire guide liner conduit. When the wire feeder close to the welding torch starts its wire feeding action, a few seconds pass before the feed assisting rear booster recognizes that feeding is required. This is due to the inherent flexibility of the wire guiding system that allows feeding of some centimeters of welding wire into the wire guiding liner conduit (or pulling it from the wire guiding liner conduit) at one end without a consequent immediate movement of the wire at the other end. This effect is known as backlash. The same effect noticeable at a start of the feeding action can be noticed at a stop of the feeding action. The wire feeder close to the welding torch will stop without the booster feeder noticing this immediately. The backlash results in the welding wire not being advanced at the welding torch with the speed and promptness actually requested. In other words, a wire pushing booster, not synchronized and not directly interacting with the wire pulling master feeder, does not promptly and accurately react to the starts and stops commands and the wire feed speed imposed by the master feeder itself and this makes the whole welding process extremely unreliable. A delayed feeding assistance by the booster at the feeding start can cause welding torch contact tip burn-backs and a delayed feeding interruption by the booster can cause the booster rolls to scratch and deform the wire surface.
Since the existing prior art independent wire feed assisting rear boosters are not directly activated by the front feeder and the rear booster pushing action is activated normally by a built-in magnetic clutch or an equivalent mechanical device which detects that wire is eventually being pulled by the front main feeder, they are often suffering from excess over heating because the rear booster feeder motor is always in torque, also after the welding action is interrupted and the wire is not being pulled by the front wire feeder; this can contribute to considerably reduce the rear booster feeder motor lifespan and can cause a fire hazard and a consequent safety issue in the welding robot cell area.
A reliable way to remotely start or stop the rear booster, and still function independently from the main pulling feeder, is represented by the prior art embodiment of a welding wire feeding system having a wire movement sensing device formed as a self-contained stand-alone unit and adapted for being mounted onto a wire guide, and an assisting feeding device for assisting the feeding welding wire depending from signals received from the wire movement sensing device. This technology is based on the idea of actively controlling a feed assisting device, which acts in a manner similar to the known slave booster feeders, by employing the wire movement-sensing device close to the “main” master feeder that is usually the wire feeder close to the welding torch. The wire movement-sensing device is represented by a small unit, which is physically independent from the master feeder and can be mounted at a suitable location along the path of the wire, preferably close to the master feeder. This solution, however, has its drawbacks because in order to make the stand-alone front motion detecting device communicate with the rear feed assist booster, it is still necessary to connect the two units through a hampering cable and this can represent an extra cost and complicate the setup inside the robot cell. Prior art inventions also suggest a simpler way for the two units to interact through a wireless communication, but this solution is not applicable in those manufacturing facilities where Bluetooth communications can interfere with other equipment. In most automotive plants, for example, wireless communications are often banned.
In one further prior art system, a wire feeding system allows a reliable control of the rear booster and the smooth feeding of a welding wire over long distances without involving a complicated or expensive system and without any need of synchronization between the master wire feeder and the assisting booster feeder. This system uses the welding wire electrode itself as the mean through which digital data and signals, like the voltage, between the front feeder connection and the back wire booster are transmitted. This permits to eliminate the use of hampering cables and to save the cost of the motion detecting device, regardless of the distance between the front pulling feeder and the back booster and the length or the path of the wire guiding liner conduit. With this particular system, the slave feeder, or booster, detects and instantly reacts to the presence of voltage passing through the welding wire as soon as the welding power source or welding machine, supplies tension and the welding arc is struck at the welding torch tip. This detection of this signal is immediate and allows to promptly start or stop the booster motor torque in connection with the actual welding action, thus preventing unnecessary and dangerous overheating of the rear booster unit, improving the accuracy of the wire boost and increasing the booster motor lifespan, with an efficiency comparable to the conventional synchronization between feeder and booster. In the GMAW (gas metal arc) and other welding processes, as soon as welding voltage and current is supplied by the welding machine and the welding arc is struck, a tension varying from 5 to 100 Volts, travels through the welding wire electrode. Consequently, the main wire feeder simultaneously starts pulling and feeding wire from the bulk container into the welding torch, since the two actions are inter-connected. This prior art system detects and exploits the presence or absence of tension signal on the welding wire, which is the equivalent of the start or stop of the main feeder, and simultaneously translates it, through the booster components and software, into a command to start or stop of the rear booster motor torque. Since the rear booster and the front main feeder are not connected and the two speeds are not synchronized, the booster software can perform a variety of additional functions like, for example, controlling the motor torque and pushing a bit more than the front feeder in order to compensate the backlash by filling with welding wire all the free space at the liner conduit curvatures, or it can stop the motor torque partially or completely after a few seconds of welding inactivity.
However some manufacturing processes and technologies like LASER welding, TIG (Tungsten Inert Gas) welding or metal spraying treatment of metal parts, do not involve any presence of current on the wire during feeding, and without voltage running on the wire during the arc, the previously described prior art invention becomes completely useless.
It is an object of the present invention to provide a wire feeding system using a stand-alone rear wire booster which can efficiently operate without any need of electronical synchronization with the front pulling wire feeder.
It is a further object of the present invention to provide a wire feeding system, which gives an immediate support to the front pulling wire feeder as soon as the front pulling wire feeder is starting to feed wire through the welding or spraying torch.